In recent trends, cell phones packaged with a digital camera are becoming quite common. With the advancement in the communication network and the reduced size of the high resolution digital camera, camera cell phones are no longer limited to just low resolution images. Instead, it is becoming more common that camera cell phones are able to take, transfer, and transmit high resolution images and video images. In fact, it is not too far off when the camera resolution will be drastically increased from its current 110K (CIF) or 330K (VGA) pixels to as much as 10 million pixels. This increase in resolution, however, greatly affects both the bandwidth and the clock requirements for the camera port in the baseband processor. For example, because the current baseband processors simply cannot keep up with the fast changing camera resolutions and required bandwidth to work with these resolutions, they must be upgraded. This, in turn, increases the cost of the device and the time to market for these new cell phones.
Moreover, the significant resultant variation in clock ranges is impractical, since the clock rate is typically limited by the baseband processors. For example, a 1.3 megapixel camera typically requires a 54 megahertz (MHz) clock for 15 frames per second, a 4 megapixel camera requires approximately 131 MHz, and a 10 megapixel camera requires approximately 300 MHz. Although many cameras include an embedded Phase Locked Loop (PLL) that allows the baseband processor to provide a slower clock, the data rate and the pixel clock coming back from the camera are nevertheless directly tied to the camera resolution. Thus, even with the PLL and the baseband processor providing 27 MHz to the camera, the actual camera pixel clock could be as high as 300 MHz for a 10 megapixel camera.
Another significant challenge is the electromagnetic interference (EMI) that results when bringing a high 131 MHz for a 4 megapixel image or 300 MHz for a 10 megapixel image from the camera to the baseband or imaging co-processor, which makes the integration of high resolution cameras into a wireless device very difficult. The challenge is even greater for wireless devices that use a clam shell (or so-called flip) form factor. In order to solve this problem, one proposed method is to serialize the interface to reduce pin count and to reduce the EMI. This approach, however, does not address the high bandwidth requirements for 4 through 10 megapixel imagers, because using the serial interface with a 10 megapixel imager will require clock rates above 1 gigahertz.
Another proposed solution is to provide more memory in the camera to hold the entire compressed image. This solution, however, is very expensive, because the memory will increase the production cost of these devices. Another proposed solution is to provide a separate port like a static random access memory (SRAM) interface or serial interface that is added to extract the compressed data from the camera. This separate port, however, is not a workable solution, since it operates with the larger memory and sometimes increases the pin count between the baseband processor and the camera module, which causes more interference from the EMI. Even if the same camera port signals are reused to retrieve the compressed data, the protocol and timing between the compressed data and the viewfinder data are incompatible, and they do not match the existing processors. This makes pulling data out of the module difficult and sometimes impossible for a given platform.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve understanding of various embodiments of the present invention. Also, common and well-understood elements that are useful or necessary in a commercially feasible embodiment are typically not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.